Our goal is to study the mechanisms of immune defense against tumors. More specifically we plan to carry out the following projects: (a) Studies on the mechanisms of macrophage activation, especially the role of prostaglandins in this reaction. (b) Isolation and purification of macrophage activating factor(s) from stimulated lymphocytes. (c) Further studies on the mechanisms of antigen recognition by T lymphocytes. (d) Studies on the mechanisms of action of lymphocyte activating factor. (e) Isolation and characterization of human leukemia specific antigens. (f) Purification and physicochemical characterization of a macrophage-membrane associated cytotoxic factor.